An Ājivaka whom the Buddha met on his way between Gayā and the Bodhi Tree, after he set out from Isipatana for the preaching of the First Sermon. Upaka questioned the Buddha on his attainments, and when the Buddha told him what he had accomplished he asked the Buddha if he were “Anantajina.” When the Buddha acknowledged it, Upaka shook his bead saying, “It may be so, friend,” and went along by another road Vin.i.8 MN.i.170–171 The Saṃyutta Nikāya SN.i.35 SN.i.60 records a visit paid to the Buddha by Upaka and six other beings born in Avihā.
He once visited the Buddha at Gijjhakūṭa and stated before him his view that whoever starts abusive talk of another, without being able to make good his case, is blameworthy. The Buddha agrees and says that Upaka himself has been guilty of this offence. Upaka protests against being caught in a big noose of words, like a fish caught as soon as he pops up his head. The Buddha explains that it is necessary for him to teach with endless variations of words and similes. Upaka is pleased with the Buddha’s talk and reports the conversation to Ajātasattu. The king shows his anger at the man’s presumption in having remonstrated with the Buddha. AN.ii.181f.
He was apparently of low caste, and Ajātasattu addresses him as “salt-worker’s boy” (loṇakārakadāraka). AN.ii.182